1. Field of the Invention
The present invention relates to an image capturing apparatus and method of controlling the apparatus. More particularly, the present invention relates to an image capturing apparatus for capturing a chart having color patches of a plurality of colors and obtaining a color-patch signal for creating a color profile, and to a method of controlling this apparatus.
2. Description of the Related Art
In digital cameras now in general widespread use, color conversion processing is executed in such a manner that color reproduction of captured image data will result in an optimum color namely a color that is faithful to the color of the subject or a color that is desired by the observer, etc. The color of a subject, however, differs greatly depending upon the light source that illuminates the subject. Accordingly, even in case of color conversion processing that has been set up so as to obtain the optimum color reproduction under a certain light source, the optimum color reproduction will not necessarily be obtained if this processing is applied to image data that has been captured under a different light source.
In a digital camera, therefore, white balance control is carried out as processing preliminary to color conversion processing. However, R, G, B or other color information that is output by the sensor of the digital camera do not necessarily correspond to the tristimulus values perceived by a human being. This is ascribable to the fact that the spectral sensitivity of each pixel of R, G, B in the digital camera does not coincide with the color matching function. If the spectral sensitivity coincides with the color matching function, then, as long as an appropriate white balance is achieved, it will be possible to obtain optimum color reproduction by a single optimum color conversion processing operation under any light source whatsoever. In actuality, however, spectral sensitivity differs from the color matching function. Therefore, in order to execute highly accurate color conversion processing, it is necessary to execute color reproduction processing that difference depending upon the light source.
In order to execute color reproduction processing that differs in accordance with the light source, it is necessary to provide color profiles, such as look-up tables for performing color conversion, for respective light sources. A known method of creating such a color profile is to capture the image of a chart, which comprises a plurality of color patches, and create the color profile based upon the captured data of each color patch (e.g., see the specification of Japanese Patent Application Laid-Open No. 2003-244464). Another example of prior art for creating a color profile of a digital camera is to display a frame for capturing color at the time of photography (e.g., see the specification of Japanese Patent Application Laid-Open No. 2006-186594).
In the conventional methods of creating a color profile described above, it is assumed that the color patches have been captured accurately. That is, it is assumed that the chart to be captured has been captured under correct exposure conditions and at a correct focus under a prescribed shooting magnification. Accordingly, if the chart has not been captured accurately, the precision of the created color profile declines or creation itself becomes impossible.
However, performing chart capture is not easy for a user who has little experience in chart capture, and often a color profile is created from a badly captured image of the chart. Finally, resulted color profile has problem in its accuracy.